Apparatus for folding a trailing panel on carton blanks

ABSTRACT

Apparatus for a paper box folding machine for folding the trailing panels of carton blanks about fold lines as the blanks travel individually and successively along a paper line. A servomotor running continuously at a relatively constant nominal angular velocity drives the input shaft to an indexer that controls, for each position of its input shaft, the angular position of its output shaft. The indexer converts continuous input from the servomotor to discontinuous motion of its output shaft. The output shaft lies below and transverse to a paper line. Radially extending fingers mounted on the output shaft are positioned below a trailing panel as the carton blank passes. The indexing means output shaft and fingers rotate rapidly so the fingers engage and fold the trailing panel and then dwell to allow the blank to exit the apparatus. Then the shaft and fingers move below the paper line to allow another blank to enter and rotate to engage a next blank in sequence. A specific embodiment includes two folding stations and the control system for operating these stations independently.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to apparatus for manufacturing folding cartonblanks and, more specifically, to apparatus for folding the trailingpanels of such carton blanks.

2. Background

In machines for folding blanks successively and individually, the blankstravel through a series of stations. Apparatus at each station performs,sequentially, some folding, gluing or other operation on individualpanels formed on the blanks as successive blanks pass that station. Aconveyor system transports the blanks past each station in seriatim,normally on a "paper line".

Folding operations require a trailing panel to be folded forward (i.e.,in the direction of travel of the conveyor) about a fold line that istransverse to the paper line. Trailing panel folding operations presentspecial problems in carton folding because the blank must pass thefolding station before the apparatus can engage and fold the panel

Some systems fold trailing panels by using a so-called "right angle"paper line. Essentially, the apparatus folds and glues all panels on thefront and sides along a first paper line Then the apparatus directs theblanks to a second paper line that runs at right angles to the firstpaper line. If the orientation of the blank in space remains the sameduring the transfer, the trailing panel on the first line becomes a sidepanel on the second line and can be folded as a convent side panel. Thisapparatus has several drawbacks. First, the transfer from one line toanother requires care often achieved by increasing the spacing betweenblanks and slowing conveyor speed. This reduces machine throughput.Moreover, right-angle systems generally require more floor area thanstraight-line systems; consequently overheads increase, so thisapparatus is more costly to operate.

There has been an effort to develop trailing panel folding stations thatoperate in a straight-line, or in-line, apparatus. The following U.S.Letters Patent disclose prior efforts:

U.S. Pat. No. 3,330,185 (1967) Annett et al

U.S. Pat. No. 3,901,134 (1975) Reizenstein et al

U.S. Pat. No. 4,119,018 (1978) Nava

U.S. Pat. No. 4,432,745 (1984) Eldridge

U.S. Pat. No. 4,539,002 (1985) Zak

U.S. Pat. No. 4,715,846 (1987) Zak

Annett et al disclose a box folding machine apparatus. A cam mechanismdriven from a shaft rapidly accelerates an arm on a head to overtake arear panel and fold it on top of a blank.

In accordance with Reizenstein et al, a clutch has an input connected tothe main drive of the folding box apparatus and an output connected to asecondary drive for an endless operating loop. A sensing means respondsas each blank passes a reference point by causing the clutch to engageand initiate motion of the endless operating loop that is synchronizedto the position of the blank. Folding fingers pivotally connect to theloop and have cam followers that engage a stationary cam. Each fingermoves into contact with a box blank at the trailing panel as the camfollower contacts the cam. A second sensing means and related apparatusdisengage the clutch when the folding finger reaches a predeterminedposition after completing the folding operation.

Nava discloses a system with a trailing edge sensor that initiates theoperation of a folding head with a cam control element. This controlelement moves folding fingers with an appropriate velocity profile toengage and fold a trailing panel The mechanism includes a shaft for thefolding heads, an idler shaft that carries the cam, a braking mechanismand a clutch.

Eldridge discloses a trailing panel folding machine with a two-armedhead that rotates one-half revolution each time it folds a trailingpanel. A drive motor and clutch-brake assembly drive the head. Theclutch-brake comprises an electromechanical or a pressure- orvacuum-operated mechanical device. A variable speed electric motorrotates the head at a speed dependent upon the length of the blanks.Alternatively it is suggested to tie the drive to the conveyor drivemotor thereby to compensate any changes in conveyor speed.

When Eldridge's clutch-brake engages, the head rotates at the speed ofthe drive for 180° (i.e., the angle needed to perform one foldingoperation). When the clutch-brake disengages, the head stops rotating. Asensor determines the position of a blank as it travels along aconveyor. The resulting position information and conveyor speedinformation establish timing for engaging the clutch-brake mechanism andinitiating a two-step folding cycle. The drive head begins at a startingor dwell position with the clutch-brake disengaged. During a first step,a signal from an electronic controller causes the clutch-brake to engageand rotate the head to fold the trailing panel and then to disengage andstop the head in an intermediate position. This allows the blank to passfrom the folding station. After another interval, that assures that theblank has cleared this station, the controller initiates the second stepduring which the clutch-brake engages to move the folding head to aseparate home position below the paper line where the head dwells inpreparation for the next blank.

The Zak-002 patent discloses a trailing panel folding apparatus in whichfolding heads connect to a drive through a clutch-brake that responds tovarious control signals. When the trailing edge of a blank passes apredetermined position, the signals cause the clutch to engage androtate folding fingers on the heads and fold the trailing panel. Thenthe stop and subsequently rotate again to a dwell position to complete atwo-step folding operation.

The Zak-846 patent discloses a trailing panel folding apparatus in whicha servomotor directly drives a shaft carrying two folding heads. Eachhead has a pair of radially extending arms that engage and fold thetrailing panels of successive blanks. A computer and programmable motorcontroller directly control the rotation and velocity profiles of theservomotor in a two-step cycle comprising a fold step and a return step.During the fold step, one arm starts below the conveyor and rotates atan appropriate time to engage the trailing panel and fold it over. In avertical position, the drive shaft dwells to allow the blank to exitfrom under the folding arm. Then the return step positions the secondarm just below the conveyor so it is oriented at the starting position.

These embodiments of apparatus for folding a trailing edge or panel havesome common characteristics. First, they all, except for the apparatuswith Zak-846 patent, contain mechanisms that must physically engage anddisengage. These operations require finite time intervals that, in part,are determined by the momentum changes inherent whenever an elementstarts and stops. This apparatus, particularly including the apparatusof the Zak-846 patent, involves significant rapid and repeated changesin momentum, particularly as the mass of the elements involved issignificant and the process is iterative in nature. These requirementscan impose limits on parameters such as minimum blank spacing andmaximum conveyor speed that individually and collectively limitthroughput.

For example, the conveyor speed for in-line apparatus is generally afunction of the capabilities of the trailing panel folding apparatus toaccelerate, engage and overtake the blank and then to stop so the foldedblank can exit. This, in turn, depends upon the physical inertia of thefolding system and the characteristics of various elements, such asmotors, used to drive the folding element. Minimum spacing betweensuccessive blanks depends, in part, upon the time interval required tomove the folding element from a dwell position above a paper line to aposition below the paper line that allows the next blank to enter thebackfolding station. This interval also depends on the physical inertiaof the folding element and its associated drive mechanism and theability of the drive system accelerate and decelerate.

SUMMARY OF THE INVENTION

Therefore it is an object of this invention to provide apparatus forbackfolding trailing panels of blanks and for increasing throughput byminimizing the mass of elements that must accelerate and decelerateduring each folding operation.

Another object of this invention is to provide apparatus for backfoldingtrailing panels in successive blanks transported along a paper line thatincreases throughput and compensates for variations in conveyor speed.

Still another object of this invention is to provide apparatus forbackfolding trailing panels in successive blanks transported along apaper line that increases throughput and compensates for variations inspacing between successive blanks.

Yet another object of this invention is to provide apparatus forbackfolding trailing panels in successive blanks transported along apaper line that is adapted for backfolding panels from batches ofdifferently sized blanks.

Yet still another object of this invention is to provide apparatus forbackfolding trailing panels in successive blanks transported along apaper line that adapts to a variety of operating conditions.

In accordance with one aspect of this invention, apparatus in abackfolding station for folding the trailing panels of successive blankscomprises a servomotor, an indexing system for rotating an output shaftwith folding finger means that engage the trailing panels, and a controlsystem. The indexing system converts input motion from the servomotorinto a predetermined discontinuous motion of the finger means thatdepends upon the position of successive blanks The synchronized foldingfinger means fold the trailing panels and then dwell until the blankexits the backfolding station. Then a new cycle begins as the servomotorand indexing system moves the folding finger means to engage thetrailing flap of a next blank in succession.

In accordance with other aspects of this invention, a control systemestablishes a nominal angular velocity for the servomotor. The controlsystem varies the average and instantaneous servomotor velocities as afunction of blank and trailing panel size, the blank velocity along thepaper line, as represented by conveyor speed, and the spacing betweensuccessive blanks. The servomotor and input portion of the indexingmechanism operate with essentially constant momentum. Only a smallportion of the mass of the indexing mechanism and its attached outputshaft are subject to rapid momentum changes, and these momentum changesare readily absorbed within the system.

BRIEF DESCRIPTION OF THE DRAWINGS

This invention is described with particularity in the appended claims.The various objects, advantages and novel features of this inventionwill be more fully apparent from a reading of the following detaileddescription in conjunction with the accompanying drawings in which likereference numerals refer to like parts, and in which:

FIG. 1 is a simplified diagram, partially in perspective form andpartially in schematic form, of a backfolding station constructed inaccordance with this invention;

FIG. 2 is a perspective view of a folding finger means for use inapparatus that embodies the invention of FIG. 1;

FIGS. 3 and 3A are perspective views of alternative embodiments offolding finger means shown in FIG. 2;

FIG. 4 graphically relates the relationship between output and inputshaft angular position for the indexing mechanism shown in FIG. 1;

FIG. 5 graphically relates output shaft velocity to input shaft positionfor the indexing mechanism shown in FIG. 1;

FIG. 6 depicts the relationship between various angular positions of thefolding finger means in FIG. 2 and blank positions as a blank passes thefolding finger means and the folding finger means backfolds a trailingpanel;

FIG. 7 is a top view of a portion of an in-line blank folding systemincorporating a specific embodiments of the invention for folding panelsat two backfolding stations;

FIG. 8 is a side view of the apparatus shown in FIG. 7;

FIG. 9 includes a series of perspective views in FIGS. 9A through FIG.9F that illustrate the effects of various operations on a blank;

FIG. 10 is a detailed view of a portion of the first backfolding stationshown in FIG. 7 and 8;

FIG. 11 is a detailed view of another portion of the backfoldingapparatus shown in FIGS. 7 and 8;

FIG. 12 is a detailed perspective view of a portion of a secondbackfolding apparatus shown in FIGS. 7 and 8;

FIG. 13 is a perspective view of the detail of another portion of thesecond backfolding apparatus shown in FIGS. 7 and 8;

FIG. 14 is a block diagram useful in understanding the operation of acontrol system for the apparatus shown in FIGS. 7 and 8; and

FIG. 15 is a block logic diagram that defines the operation of thecontrol system shown in FIG. 14.

DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

FIG. 1 is a diagrammatic view of a single backfolding station toillustrate the relationship between various elements of such a stationand a paper line 20 including continuous conveyor belts 20a and 20b. Inactual practice, a typical paper line 20 comprises one or more sets ofvertically aligned belts spaced along the length of the paper line 20.The disclosed backfolding station also includes a drive motor 21 and atachometer 22 or other device that generates a signal indicatingconveyor speed. Typically the drive motor 21 connects to the paper line20 through a series of shafts and drive transmissions that are not shownhere for purposes of clarity.

A backfolding station 23 comprises an output shaft 24 that is transverseto and below the paper line 20, so blanks pass above the shaft 24 asthey travel along the paper line 20. The shaft 24 carries two or morefolding finger assemblies 25, each folding finger assembly comprising ablock and single finger. A journal bearing assembly 24a supports the farend of the output shaft 24 as shown in FIG. 1.

There are many possible configurations for the folding finger assembliesusing either fixed length or variable length fingers The followingdescription of three specific embodiments provides an understanding ofthe important features of these fingers and the interaction between thefingers and the remaining apparatus. For example, FIG. 2 discloses oneembodiment of a folding finger assembly 25 that is particularly adaptedfor use with blanks having relatively short trailing panels as measuredtransversely to the fold line (i.e., less than 3.5 inches deep). Itcomprises a block 26 with a bore or sleeve 27 for mounting to the outputshaft 24 by conventional means. A single finger 30 includes a flatportion 31 at one end Rivets, machine screws or other conventional meansaffix the flat portion 31 to an edge surface 32 of the block 26. Thebalance of the finger assembly 30 has an "S" shape. A first portion 33or base of the "S" produces an offset away from the

Referring again to FIG. 1, a control system 52 controls the servomotor50 in response to a number of inputs. These inputs include the paperline speed signal generated by the tachometer 22, velocity and positionsignals from the servomotor 50 and blank position signals generated by aphotodetector system. FIG. 1 also discloses a photodetector system inwhich a lamp 53 directs light across the paper line 20 to actuate adetector 54 between individual blanks. Other photodetector systems, suchas reflector systems, or other position sensing systems can besubstituted for the specifically disclosed system in FIG. 1. Inaddition, FIG. 1 discloses only a single photodetector system. It isalso possible to use multiple photodetector systems with the generationof independent blank position signals, as will become apparent later. Aninput keyboard 55 enables an operator to define input parameters such asbox length, flap length and finger size.

In FIG. 1 the servomotor 50 has a horizontal output shaft 56 thatdirectly couples to an input shaft 57 for the indexer 51. FIG. 1 alsodepicts a direct coupling for clarity; in an actual embodiment, a timingchain couples the input shaft 57 and the output shaft 56. Further, thiscoupling can provide a speed reduction In one particular embodiment, thecoupling provides a 2:1 speed reduction; that is, the servomotor outputflat surface 32 while an inverted "U" shaped portion 34 completes the"S" at a rounded tip 35.

FIGS. 3 and 3A depict alternative folding finger assembly for use withblanks having large trailing panels (i.e., in excess of 3.5 inchesdeep). The folding finger assemblies in FIGS. 3 and 3B contain similarblocks 26 with bores or sleeves 27 and supporting surfaces 32. In theembodiment of FIG. 3 a single finger 40 has a flat end portion 41;rivets, machine screws or similar devices secure the end portion in 41to the edge surface 32 of the block 26. One end of an elongated section42 connects to an offset 43 that produces an elongated bottom portion ofan "S" shape. A top portion 44 of the "S" and rounded tip 45 connect tothe other end of the central section 42. The top portion 44 and tip 45are similar to the end section 34 and rounded tip 35 in FIG. 2.

In FIG. 3A, a finger 46 has an end portion 47 that connects to the edgesurface 32. A central offset portion 48 interconnects the end portion 47and a straight section 49 that terminates in a rounded tip 49a. Bends atthe offset 48 normally orient the straight section 49 so it is obliqueto the plane of the end section 47 and is directed back to an extensionof that plane. The longer distance between the central axes of theapertures 27 and the output shaft 24 and the rounded tips 45accommodates blanks with larger or deep, trailing panels. shaft 56rotates two revolutions for each revolution of the indexer input shaft57 and the output shaft 24.

Before discussing a specific embodiment in detail, it will be helpful toreview the problems of prior art apparatus, discuss the principles ofoperation for the apparatus in FIG. 1 in terms of an elementary modeland then the adaptation of the elementary model to practical apparatus.The previously described prior art apparatus accelerates and deceleratesfolding fingers between zero, or dwell, momentum and some maximummomentum. Some prior art apparatus uses clutch-brake mechanisms tocouple and decouple a folding finger assembly from a drive motor. Thedrive motor may comprise an independent motor or a power take-off fromthe main drive for the paper line.

Other prior art identifies problems with such clutch-brake mechanismsincluding an inability to vary the velocity of the folding fingersduring each folding operation. The prior art substitutes a servomotordrive for both the drive motor and the clutch-brake mechanism toovercome this problem and to permit such velocity variations. However,it is necessary to accelerate and decelerate the entire rotating mass ofthe folding apparatus between the zero and maximum velocities duringeach folding operation, including the servomotor rotor with itssignificant mass. From a practical standpoint, it is difficult to obtainservomotors that operate under the desireable high throughput conditionsfor paper box folding apparatus and provide the required accelerationand deceleration and attendant major momentum changes encountered intrailing panel folding operations. The apparatus shown in FIG. 1 andconstructed in accordance with this invention overcomes both theconstant velocity problem of clutch-brake mechanisms and the significantmomentum change problem of direct servomotor drive apparatus byinterposing the indexer 51 intermediate the servomotor 50 and thefolding finger output shaft 24.

The indexer 51 establishes a specific relationship between each angularposition of its input shaft 57 and the output shaft 24. In one specificembodiment the input mechanism for the indexer comprises a cam attachedto the shaft 57. The cam has a concave globoidal shape and acircumferential tapered rib. A hub with a number of radially mounted camfollowers drives the output shaft 24. Specifically, as the tapered ribrotates, the followers translate any displacement of the rib axiallyalong the shaft 57 into rotary motion of the shaft 24. The use of pluralribs on the cam surface enable the followers to rotate the shaftcompletely. Such devices are known in the art; one such device ismanufactured by Ferguson Machine Company of St. Louis, Mo.

The indexer 50 effectively decouples the significant mass of theservomotor 50 from the minimal mass of the output shaft 24 and thefolding fingers 25, so momentum changes during each folding operationare small in comparison with the average momentum of the entireassembly. Specifically, the indexer cam and its input shaft 57 connectdirectly, or indirectly through a timing chain or other speed reductiondevice, to the servomotor output shaft 56 with its connected rotor.Lands on the cam in the indexer produce the necessary velocity changesthrough the cam followers, but for purposes of understanding theelementary model, the cam, its input shaft 57 and the servomotor rotorand its output shaft 56 rotate with an essentially constant velocity andhence an essentially constant momentum. The mass of the cam follower inthe indexer 51 the output shaft 24 and folding fingers is a smallpercentage of the total mass that rotates during a folding operation.Thus, the momentum changes associated with the accelerations anddecelerations during each folding operation are small in comparison withthe total momentum of the folding apparatus. If a cam were speciallyconstructed for a specific blank configuration, the momentum changesthat would occur during each folding cycle could be made to balance orsubstantially balance. If such a balance were achieved, the servomotor50 would operate at a substantially constant velocity even during eachrotation of the output shaft 24 and folding finger assemblies 25.

FIGS. 4 through 6 depict operating conditions for a typical indexingmechanism and folding apparatus that is useful in understanding thisinvention. In these Figures, the reference numerals P1 through P18 referto specific positions of a blank 60 as it moves along the paper line 20with respect to the output shaft 24. The positions are equidistantapart, so the intervals are also equal in time, assuming the paper line20 runs at constant speed. Each of the numerals P1 through P18 refersalso to a specific angular positions of the input and output shafts andfinger 40 as shown in FIG. 6. A P1 position represents a position with afixed angular displacement before the fingers 25 engage a trailingpanel. A P13 position represents the position at which the finger 40dwells while a blank 60 exits the backfolding station. This is a "HOME"position. The intersection of the ordinate and abscissa in FIGS. 4 and 5represents a position of the finger 40 intermediate the dwell positionP13 and the next position P18 shown in FIG. 6.

An operating cycle begins with the finger 40 in the dwell, or "HOME",position. During the interval from P13 to P17 the profile of the cam andrib in the indexing mechanism remains axially stationary, so the outputshaft 24 is stationary even though the input shaft 57 continues torotate.

When the input shaft 57 reaches an angular position corresponding toposition P17, the rib on the cam shifts axially and accelerates theoutput shaft 24 to a nominally constant velocity until the output shaft24 reaches the position P4. The control system determines the velocityso the finger 40 arrives immediately below a trailing panel 61 of a nextblank 60 travelling along the paper line 20.

During the interval form P4 through P0 the output shaft 24 acceleratesto a maximum velocity, and the finger 40 rapidly moves the panel 61 to anearly vertical position with to the blank 61 about a fold line 62. Frompositions P9 through P13, the output shaft decelerates to dwell atposition P13. As the finger 40 decelerates, it continues to fold thepanel 60 as the surface of the finger 40 moves to a position thatparallels to the paper line. Then the finger 40 begins its dwell at the"HOME" position P13 until the blank clears the backfolding station.

From the foregoing discussion, it will be apparent that the fingermechanism 25 turns at an essentially constant velocity during theintervals from P17 through P4 under steady-state conditions. Thus, nochange in momentum occurs in the entire backfolding station during thatinterval. The momentum does change from positions P5 through P18 becausethe finger 40 accelerates, decelerates, dwells and accelerates again. Inaccordance with this invention, however, the change in momentum islimited in absolute terms because only the cam followers and hub in theindexer 51 and the output shaft 24 and finger assemblies 25 undergoacceleration and deceleration.

As previously stated, the mass of these elements as a percentage of thetotal mass of the rotating portions of the servomotor 50, indexer 51,output shaft 24 and finger assemblies 25 is small, so the change inmomentum, as a percentage of total momentum, is also small.

If the conveyor speed and carton spacing were to remain constant, theservomotor output shaft 56 would turn at a relatively constant velocityduring each folding operation and over successive folding operations.These conditions rarely exist in actual apparatus; it just is notpossible to guarantee absolutely constant conveyor speed or constantspacing. Therefore, the control system increases or decreases thevelocity of the servomotor output shaft 56 during each folding operationto compensate such changes. For example, the control system increases ordecreases servomotor velocity if, after the trailing edge of a blankpasses the detector 54, the paper line speed increases or decreases,respectively. For a given conveyor speed, the control system alsoincreases or decreases servomotor velocity to compensate for decreasedor increased spacing between successive blanks.

More specifically, the control system monitors the conveyor speed signalfrom the tachometer 22, the blank detector signal from the photodetector54, and the position of the servomotor 50 as shown in FIG. 1. Theresulting servomotor velocity adjustments are incremental. Duringstartup the control system 52 utilizes conveyor speed from thetachometer 22 and the arrival of the leading and trailing edges of ablank as detected by the photodetector 54 to determine the time neededfor the blank to reach the P4 position and the time required for theblank to pass through the system. The control system 24 again adjuststhe speed of the servomotor 50 to compensate variable conveyor speed andsynchronize backfolding operations to conditions of the paper line 20.

It also is possible to "jog" the folding system incrementally and obtainappropriate operation in the backfolding stations. In this operatingmode, the servomotor does start and stop during each operating cycle.However, the "jog" made is a diagnostic mode and the intervals requiredto accommodate large changes in angular momentum are not detrimental.

Thus, backfolding apparatus constructed in accordance with thisinvention has several advantageous characteristics. During normaloperations, the rotary portion of the servomotor and the input cam ofthe indexer operate at a steady-state condition. The portions of theapparatus that do undergo significant acceleration and decelerationunder steady state conditions (i.e., the cam follower, output shaft andfingers) during each folding cycle have minimal mass, so the totalchange in momentum is small in comparison with the total momentum of thebackfolding apparatus. Even when the control system changes theservomotor speed to accommodate variations in operating conditions suchas paper line velocity and blank spacing, the speed of the controlsystem normally alters servomotor speed only as a small percentage ofits nominal speed. Even during such variations, the servomotor runscontinuously, but at slightly changed velocities, so no significantchanges in momentum occur even as such operating conditions change.These characteristics improve throughput because the paper line 20 canoperate at a higher speed with closer blank spacing than can be attainedwith prior art systems.

Apparatus operated in accordance with the foregoing description couldoperate with a given blank configuration, but would not operate with allof the advantages of this invention for different blank configurations.Trailing panel folding apparatus must accommodate a wide range of cartonconfigurations In accordance with another aspect of this invention, itis possible to adapt the apparatus with diverse blanks by controllingservomotor velocity control continuously during each folding operation.

In one embodiment, each folding operation, as shown in FIG. 6, comprisesthree segments. Segment A corresponds to the positions from P13 wherethe folding fingers 25 dwell to position P18 where the folding fingers25 pass just below the paper line 20. Segment B corresponds to positionsP18 to a position near position P4 representing the interval duringwhich the folding fingers rotate from a point just below the paper line20 to a point just before they pass the paper line 20 in an upwarddirection (as applied to FIG. 6) and strike the trailing panel 61.Segment C corresponds to the interval during which the folding fingers25 rotate from the position corresponding to the end of Segment B to thedwell position at position P13; the folding fingers 25 fold the trailingpanel 61 during the interval corresponding to Segment C.

As previously described, the control system 52 establishes average ornominal operating conditions for the servomotor 50. Further, the controlsystem can vary, or offset, those conditions to compensate conveyorspeed and spacing variations. In accordance with this invention, thecontrol system 52 can also vary or offset servomotor operatingconditions during each folding operation. For Segment A, the controlsystem 52 establishes the velocity as a function of the paper line speedand blank spacing. More specifically, the control system determines thetime available and required velocity in response to the interval thatwill expire with no blank between the folding fingers 25 and the paperline. This time is a function of spacing between the last blank that wasfolded and the next blank in succession and the speed of the paper line20. The velocity during Segment B is a function of the carton length,the panel length and the conveyor speed. The control system must controlthe servomotor 50 so it moves the folding fingers 25 to the position P4during the time that it takes a strike point on the trailing flap to bepositioned above the folding finger 25. The exact location of the strikepoint can be selected arbitrarily, but a position that is abouttwo-thirds of the distance from the fold line 62 to an edge of thetrailing panel provides satisfactory results. The velocity duringSegment C is a function of the size of the trailing panel being folded.More particularly, the distance from a fold line 62 to the strike pointon a trailing panel 61 and conveyor speed determine the time required tomove the fold line 62 to the exit of the folding station.

Thus, during normal operations, the control system establishes a nominalvelocity for the servomotor dependent upon carton size, panel size,paper line velocity, blank spacing and other factors. The control systemalso calculates variations from this nominal velocity for each segmentduring each folding operation. However, these variations represent onlya small fraction of the nominal velocity, so the momentum changes alsoare minor. It has been found that appropriate adjustments of the variousoperating parameters will minimize any energy imbalances caused by suchvelocity variations during each folding operation. The only limit is thephysical design of the servomotor, particularly the current limits thatthe manufacturer imposes. These limits determine the maximum rate ofchange of momentum that the servomotor can tolerate. However,commercially available servomotors are available that are operable withthis invention over a wide range of carton configurations and operatingconditions.

With this understanding of the operation of the system shown in FIGS. 1through 6 it will be helpful to now describe a specific implementationof this invention in a paper line utilizing two backfolding stations. InFIGS. 7 and 8, blanks move from right to left along the paper line 20.The folding apparatus comprises a frame 101 with a blank feeder 102, atthe right end thereof, that feeds blanks 103 onto a first conveyor 104individually and successively at more or less predetermined intervalsand spacing. Such devices are well known in the art.

As the blanks 103 move from the blank feeding station 102, theyencounter a first backfolding station 105. A conveyor system 106connected to a main drive motor (not shown) moves each blank past thefirst folding station 105 to a second backfolding station 107. Aconveyor 108 then moves each blank through the second folding station107 to other folding apparatus downstream.

As shown in FIG. 9A, a blank 103 typically has a central panel 111 witha leading edge panel 112 for being folded about a fold line 113. Leadingedge corners or end panels 114 fold about fold lines 115; a cut 116separates the leading edge panel 112 and corners 114 so the foldingoperations are conducted independently on the panel 112 and the corners114. The leading edge panel 112 additionally has a diagonal fold line117 that intersects the fold line 113 and cut 116 to define an outertriangular section 118 as a gluing tab 118. The blank 103 additionallyincludes side panels 120 formed at fold lines 121. A trailing edge panel122 extends along a fold line 123; trailing corners or end panels 124,along fold lines 125. Cut lines 126 separate the trailing edge panel 122and the corners 124. Diagonal fold lines 127 on the trailing edge panel122 define glue tabs 128 that are analogous to the tabs 118.

FIG. 9A depicts a blank 103 as the blank feeder 102 in FIGS. 7 and 8dispenses it onto the conveyors and as it reaches the first backfoldingstation 105. The first backfolding station 105 folds the trailing panel122 forward on the fold line 123 and grabs the triangular glue tabs 128at the ends of the trailing panel 122, folding them back over the panel122 as shown in FIG. 9B. Other elements, as will be described, engagethe leading edge panel 112 and fold it back along its fold line 113.Other apparatus engages the triangular glue flaps 118 as shown in FIG.9C. Thus the blank exits the first backfolding station 105 as shown inFIG. 9D with the leading and trailing edge panels 112 folded over thetop of the central panel 111 along their respective fold lines 113 and123. In addition the glue tabs 118 and 128 overlie the panels 112 and120, respectively.

The second folding station 107 folds the corners 114 and 124. Initiallythe apparatus folds the trailing corners 124 forward on their fold lines125 as shown in FIG. 9E. Then the other apparatus in the station foldsthe corners 114 back on their fold lines 115. The blank 103 exits thesecond station 107 with the configuration shown in FIG. 9F.

Referring specifically to FIGS. 7, 8 and 14, the first backfoldingstation 105 comprises folding fingers 130 mounted to an output shaft 131driven by a cam operated indexing system 132 and servomotor 133. Adistributed control system 134 provides operator input for controllingthe operations of the fingers 130 and the second backfolding station107. A single photodetector 135 connects to the distributed controlsystem 134 by means of a cable 136 shown specifically in FIGS. 7 and 8.

Now referring to FIGS. 7, 8 and 10, the conveyors 106 engage the blank103 along the edge panels 120. FIG. 10 depicts the fingers 130 in thepreviously described dwell position engaging the trailing panel 122after folding it. In addition fingers 140 at ends of the trailing panel122 engage the tabs 128 to begin folding them. Still referring to thestation 105, as the blank progresses, first hold down fingers 141 shownin FIG. 10 engage the trailing edge panel 122 to maintain itsorientation as the blank 103 moves downstream. Another finger 139engages the leading edge flap 112 and holds it stationary as the blank103 advances thereby to fold the leading edge panel 112 about the foldline 113. Slides 143 at each side of the station 105 fold the tabs 118about the diagonal fold lines 117. Hold down fingers 144 engage the gluetabs 118. Thus, the operations shown in FIGS. 10 and 11 produce a blank103 as shown in FIG. 9D.

Now referring to the second folding station 107 shown in FIGS. 7, 8, 12and 13, the conveyor belt system 108 is displaced inwardly from theconveyor system 106 shown in FIGS. 10 and 11 to engage the blanks 103 onlines through the glue flaps 118 and 128. This effectively maintains theleading and trailing edge panels 112 and 122 in their folded positions.

As shown in FIG. 14, an output shaft 151 drives a second set of fingers150 from a cam operated indexer 152 and servomotor 153. The distributedcontrol system 134 provides the appropriate signals for the servomotor153 independently of servomotor 133. The fingers 150, shown in the dwellposition in FIG. 12, have folded the corners 124 forward about the foldlines 125. As shown in FIG. 13, fingers 154 fold the corners 114 aboutthe fold lines 113 thereby to complete the folding operation and producea final blank that leaves the folding station 107 in the form shown inFIG. 9F.

Now referring to FIG. 14, the distributed control system 134 receivessignals from and transmits a number of signals to the backfoldingstations 105 and 107. The distributed control system 134 includes inputcircuits in the form of various interfaces for receiving signals fromthe tachometer 22, the position detector 135, and from servo amplifiers155 and 156 and other devices such as encoders 157 and 158 that provideBF1 and BF2 HOME signals that correspond to predetermined positions ofthe fingers 130 and 150 respectively. Typically the HOME positioncorresponds to the P13 position in FIG. 6. The signals from the servoamplifiers 155 and 156 represent the position and velocity of each ofthe servomotors 133 and 153, respectively. A processor 161 converts thisinformation, along with information from the input keyboard 162, intosignals for motion control circuitry 163. The motion control circuitry163 comprises dedicated processing elements that calculate the controlsignals for the servomotors 133 and 153 independently. The processor 161routes corresponding signals to the amplifiers 155 and 156 throughoutput circuits 164. A display 165 provides feedback information for theoperator. A power supply 166 provides power for the system.

The components for a distributed control system shown on FIG. 14 arereadily available. One such control system can be configured fromcomponents of Reliance Electrical Industrial Co. of Cleveland, Ohio. Theinterconnection and programming of such a system will be apparent fromthe following discussion:

Before discussing the operation of the control system shown in FIG. 14,it will be helpful to list known relationships, as follows:

1. The distances from the photodetector 135 to the axes of the outputshafts 131 and 151 are known and fixed. It is also possible to utilizeseparate photodetectors for each backfold station.

2. The tachometer 22 reliably indicates the speed the blanks travelalong the paper line 20.

3. The length of a blank and the size of its trailing panel are bothprovided through the input keyboard 162.

The processor 161 and the motion control circuit 163 use input signalsalong with signals from the amplifiers 155 and 156 for calculating, onan iterative and continuing basis.

1. The time interval before each blank that passes the photodetector135, or the respective one of multiple photodetectors, in successionreaches either the station 105 or 107.

2. The time required to move each of the fingers 130 or 150 from aposition corresponding to the position P4 in FIG. 6 so the arm fingersengage a trailing panel or corners at an appropriate time. Conveyorspeed determines the time available to move the fingers.

3. The time interval to move the fingers from position P4 to positionP13 and the velocity and acceleration profiles required during thisinterval.

The circuitry and programs of the distributed control system 134 shownin FIG. 14 control each of the servomotors 133 and 153 independently.The following description is limited to the discussion of a singlebackfolding station, namely backfolding station 105. The processes thatthe distributed control system 134 uses to control the servomotors 133and 153 independently are themselves independent processes run insequence. However, the distributed control system 134 operates at asufficiently high speed that in terms of the time intervals involvedwith the backfolding stations, the independent processes appear to occursimultaneously and in parallel.

FIG. 15 describes the basic operations by which the processor 161 andmotion control circuit 163 provide the various control signals for thebackfolding stations. In accordance with the conventional techniques,the processor 161 initializes the system in step 170 thereby toestablish initial variable and register values and provide initialinformation on the display 165. Then the processor 161 "waits" foradditional input from the keyboard 162 and the beginning of a job.

At the beginning of each job, an operator uses the input keyboard 162 toprovide information that the distributed control system 134 utilizes toestablish supplemental and intermediate values. This informationincludes blank length, trailing panel length, finger size and similarinformation. The distributed control system 134 also uses otherinformation that may be stored in the processor for a particular machineor provided through the input keyboard 162. This includes measuredinformation, such as the distance from the photodetector system 135 tothe center line for each of the output shafts 131 and 151 and thedistances between each of the output shafts and a point at which thefingers first strike the trailing flap (i.e., at the P4 position in FIG.6). The distributed control system 134 also calculates various othervalues based upon this input and measured data. In one specificimplementation at any given time the distance a blank must travel toreach a predetermined point is calculated as (1) the measured distancefrom the photodetector system 135 to the strike point minus (2)one-third of the trailing flap length minus (3) the actual distancetraveled.

After an operator supplies all the information and starts the paperline, step 171 awaits for the arrival of a blank at the photodetectorsystem 135. In addition the programs associated with backfolding station105 await the arrival of the finger assembly at the home positionrepresented by the BF1 HOME signal.

When this occurs, the processor 161 and motion control circuit 163 usestep 172 to determine if any default conditions exist. Normally noneexist so the motion control circuit 163 performs two functions and thesemay be performed by hardware in parallel.

Whenever the motion control circuit 163 detects the arrival of a blankat the photodetection system 135 in step 173, step 174 calculatesinformation that establishes the velocity of the output shaft so thatthe fingers 130 strike the trailing panel at the appropriate positionbased upon paper line velocity. In parallel step 175 monitors the BF1HOME signal. When the encoder 157 produces this signal, step 176calculates information for moving the fingers 130 from the HOMEposition.

Regardless of the control paths the processor 161 uses in performingsteps 173 through 176, step 177 updates the monitor screen and thencontrol returns to step 172 to monitor any default and to begin anotherduration.

If a fault occurs, step 172 immediately branches to step 180 as errorcondition. In this embodiment step 180 stops the backfolding operationfor that blank and returns to step 171 to await a next blank. Otherfault responses can be used.

Therefore, the processor 161 and motion control circuit 163 utilizesignals that represent various conditions in each backfolding stationwith respect to each blank entering each backfolding stationindependently. If the paper line velocity and blank spacing arerelatively constant, the control system drives the servomotors 133 and153 at a relatively constant velocity. During each blank folding cycle,the distributed control system 134 causes amplifiers 155 and 156 totransfer additional energy to the servomotors 133 and 153 during theacceleration of the output shafts 131 and 151 so the servomotors remainat a constant velocity. During decelerations, the distributed controlsystem 134 reduces the energy being transferred to the servomotors 133and 153 to compensate for the decreased momentum introduced by theindexing system so that the servomotor continues to rotate at a constantvelocity The distributed control system 134 only changes the velocity ofthe servomotors 133 and 153 to compensate uneven blank spacing or paperline velocity changes.

The implementation of the foregoing control system described withrespect to FIGS. 14 and 15 depends upon the particularly selectedequipment utilized in the distributed control system 134. Typically sucha distributed control system comprises a programmable controller andrelated equipment that requires programming. As such programs aredependent upon the selected equipment and any specific implementationwill be apparent from the foregoing description, no specific embodimentof such a program is included in this description.

In summary, there has been disclosed backfolding station that overcomesmany of the problems encountered with prior art apparatus. A systemconstructed in accordance with this invention allows the backfoldingsystem to operate at a substantially constant angular momentum with thechanges in momentum representing a small portion of the total momentumof the system. As a result, the apparatus, operates with greaterthroughput and minimal overhead.

This invention has been disclosed in terms of certain embodiments. Itwill be apparent that many modifications can made to the disclosedapparatus without departing from the invention.

Therefore, it is the intent of the appended claims to cover all suchvariations and modifications as come within true spirit and scope ofthis invention.

What is claimed as new and desired to be secured by patent of the UnitedStates is:
 1. In a paper box folding machine for forming individuallyand successively carton blanks into folded cartons, said machineincluding conveyor means for transporting successive blanks at apredetermined nominal speed and spacing along a paper line andbackfolding means for folding a trailing panel of each blankindividually and successively forward about a fold line transverse tothe paper line, the improvement of a said backfolding apparatuscomprising:A. indexing means having an input shaft and having an outputshaft transverse to and disposed below said conveyor means, saidindexing means establishing a predetermined angular position of saidindexing means output shaft for each angular position of said inputshaft whereby repeatable linear and non-linear relationships existbetween the speeds of said input and output shafts, B. servomotor meansfor driving said indexing means input shaft continuously, C. fingermeans connected to said indexing means output shaft having a radiallyextending finger for engaging and folding the trailing panels of eachsuccessive blank forward about a respective fold line as each blankpasses said backfolding apparatus, and D. control means for operatingsaid servomotor means to drive said indexing means input shaft at anominally constant angular velocity established by the nominal blankspacing and the nominal speed of said conveyor means.
 2. A backfoldingapparatus as recited in claim 1 wherein said conveyor means is subjectto speed variations and said control means includes speed signal meansfor generating a conveyor speed signal dependent upon the speed of saidconveyor means, said control means altering the speed of said servomotormeans and said indexing means input shaft in response to the signal fromsaid speed signal generating means.
 3. A backfolding apparatus asrecited in claim 1 wherein the spacing between successive blanks canvary and said control means includes reference signal generating meansfor generating a position signal each time a blank passes apredetermined position along the paper line, said control means varyingthe speed of said servomotor means and said indexing means input shaftin response to reference signal generator means indicating a spacingvariation.
 4. A backfolding apparatus as recited in claim 3 wherein saidconveyor means is subject to speed variations and the spacing betweensuccessive blanks can vary, said control means additionally includingspeed signal generating means for generating a conveyor speed signaldependent upon the speed of said conveyor means, said control meansvarying the speed of said servomotor means and said indexing means inputshaft in response to the conveyor speed and position signals thereby toposition the finger means below a trailing panel when the trailing paneloverlies said finger means.
 5. A backfolding apparatus as recited inclaim 4 wherein said control means additionally includes input means forproducing inputs for said control means representing carton blank andtrailing panel sizes, said control means additionally being responsiveto said input means for varying the speed of said servomotor means andthe indexing means input shaft.
 6. A backfolding apparatus as recited inclaim 5 wherein the machine runs in a batch mode in which each batch ofcarton blanks has the same configuration, said backfolding apparatusbeing adapted to operate with different batches defined by a range ofblank configurations and sizes and said finger means includes a basemember mounted to said indexing means output shaft and means forsecuring one of a predetermined number of fingers to said base member,said input means identifying the selected finger to said control means.7. A backfolding apparatus as recited in claim 6 wherein said indexingmeans output shaft has a plurality of said finger means attachedthereto.
 8. A backfolding apparatus as recited in claim 4 wherein saidindexing means defines, for each continuous revolution of said inputshaft, a discontinuous revolution of said indexing means output shaftincluding a first interval during which said finger means dwells, asecond interval during which said finger means moves below the paperline, and a third interval during which said finger means acceleratesand decelerates to fold the trailing panel.
 9. A backfolding apparatusas recited in claim 8 wherein said indexing means drives said outputshaft at a substantially constant speed during the second interval andvaries the velocity between a maximum and zero during the thirdinterval.
 10. A backfolding apparatus as recited in claim 4 wherein saidcontrol means includes programmable controller for setting a nominalspeed for said servomotor means dependent upon a nominal speed for saidconveyor means and having a first program for altering the speed of saidservomotor means in response to changes in conveyor speed thereby tosynchronize said indexing means output shaft with conveyor speed.
 11. Abackfolding apparatus as recited in claim 10 wherein said programmablecontroller means has another program for altering the nominal speed ofsaid servomotor means in response to said reference signal generatingmeans thereby to synchronize said indexing means output shaft to theposition of successive blanks notwithstanding the spacings betweensuccessive blanks.
 12. In a paper box folding machine for formingindividually and successively carton blanks into folded cartons, saidmachine including a conveyor means for transporting successive blanks ata predetermined nominal conveyor speed and predetermined nominal spacingbetween successive blanks along a paper line, each blank having atrailing central panel and separately foldable trailing end panels andbackfolding apparatus for folding said trailing central and end panelsof each individual and successive blank forward about the respectivefold lines, said backfolding apparatus comprising:A. A first foldingstation for folding one of the trailing central and end panels and asecond folding station for folding the other of the trailing central andend panels, each of said first and second stations being spaced alongthe paper line and including:i. indexing means having an input shaft andhaving an output shaft transverse to and disposed below said conveyormeans, said indexing means establishing a predetermined angular positionof said indexing means output shaft for each angular position of saidinput shaft whereby repeatable linear and non-linear relationships existbetween the velocities of said input and output shafts, ii. servomotormeans for driving said indexing means input shaft continuously, and iii.finger means connected to said indexing means output shaft having aradially extending finger for engaging and folding the correspondingones of the trailing central or end panels of each successive blankforward about a respective fold line as each blank passes one of saidfolding stations, and B. control means operating independently each saidservomotor means to drive said corresponding indexing means input shaftat a nominally constant angular velocity established by the nominalspacing and the nominal speed of said conveyor means.
 13. A backfoldingapparatus as recited in claim 12 wherein said conveyor means is subjectto speed variations and said control means includes speed signal meansfor generating a conveyor speed signal dependent upon the speed of saidconveyor means, said control means independently altering the speed ofeach said servomotor means and said corresponding indexing means inresponse to the signal form said speed signal generating means.
 14. Abackfolding apparatus as recited in claim 12 wherein said control meansincludes reference signal generating means for generating a positionsignal each time a blank is at a predetermined position along the paperline, said control means independently varying the speed of each saidcorresponding servomotor means and indexing means input shaft inresponse to the position signal from said reference signal generatormeans.
 15. A backfolding apparatus as recited in claim 14 wherein saidconveyor means is subject to speed variations and the spacing betweensuccessive blanks can vary, said control means additionally includingspeed signal generating means for generating a conveyor speed signaldependent upon the speed of said conveyor means, said control meansindependently varying the speed of each of said servomotor means andcorresponding indexing means input shaft in response to the conveyorspeed and position signals thereby to position a corresponding fingermeans at each of said backfolding stations independently below atrailing panel when the trailing panel overlies said finger means.
 16. Abackfolding apparatus as recited in claim 15 wherein said control meansadditionally includes input means for producing inputs for said controlmeans representing carton and trailing panel size, said control meansadditionally being responsive to said input means for varyingindependently the speed of each said servomotor means and correspondingindexing means input shaft.
 17. A backfolding apparatus as recited inclaim 16 wherein the machine runs in a batch mode in which each batch ofblanks has the same configuration, said backfolding apparatus beingadapted to operate with different batches defined by a range of blankconfigurations and sizes and each said finger means includes a basemember mounted to said indexing output shaft and means for securing oneof a predetermined number of fingers to said base member, said inputmeans identifying the selected finger to said control means.
 18. Abackfolding apparatus as recited in claim 17 wherein each said indexingmeans output shaft has a plurality of said finger means attachedthereto.
 19. A backfolding apparatus as recited in claim 15 wherein eachsaid indexing means defines, for each continuous revolution of saidinput shaft, a discontinuous revolution of said indexing means outputshaft including a first interval during which said corresponding fingermeans dwells, a second interval during which said finger means movesbelow the paper line, and a third interval during which said fingermeans accelerates and decelerates to fold the corresponding ones of thetrailing central and corner panels.
 20. A backfolding apparatus asrecited in claim 19 wherein each said indexing means drives said outputshaft at a substantially constant speed during the second interval andvaries the speed between a maximum and zero during the third interval.21. A backfolding apparatus as recited in claim 15 wherein said controlmeans includes a programmable controller means for setting independentlya nominal speed for each said servomotor means dependent upon a nominalspeed for said conveyor means and having first programs for alteringindependently the speed of each said servomotor means in response tochanges in conveyor speed thereby to synchronize independently each ofsaid indexing means output shaft with conveyor speed.
 22. A backfoldingapparatus as recited in claim 21 wherein said programmable controllermeans has other programs for altering the nominal speed of saidservomotor means independently in response to said reference signalgenerating means thereby to synchronize independently each said indexingmeans output shafts to the position of successive blanks notwithstandingthe spaces between successive blanks.